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High levels of static in sound

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  • #11869 Reply
    Nate
    Guest

    Through both the internal speaker and headphones, I hear a lot of static with the volume all the way down (subtle with speaker but very noticeable with headphones). The static persists at the same level as I increase the volume. I’m running off a battery to eliminate the possibility of a poor quality 9V adapter. I have no midi cable connected either. Is this expected behavior? If not, what can I do to investigate and eliminate the static?

    #11879 Reply
    brach
    Moderator

    Are you talking about distortion or static (as in crackles you hear when your radio isn’t tuned to a particular station)?
    Have you tried it with an external power supply to ensure that the problem isn’t with the battery (that may be low in charge)?
    There is a noise floor on the Macchiato, but it should be very low compared to the audio signal you get; and you should get basically no sound when the volume is all the way down. If you are getting some sound with the volume down then that means the problem is with one of the components after the volume pot. Go through the schematic and just check to make sure all the components after the volume pot are correct and installed properly. The problem is most likely the LM386 audio amp or associated components.
    -Brach

    #12609 Reply
    Nate
    Guest

    My Macchiato produces a lot of hiss. It’s much more than all my other synths. It’s apparent from the moment it’s powered up. I can hear the hiss both while the instrument is and is not playing. The hiss is at the same level when the volume is all the way down and all the way up. I’ve tried both a new battery and my Zuma power supply, neither have any affect on the hiss.

    Is there a schematic for the amp section available? I can’t read all the paths on the board. All my components are installed correctly and nothing looks damaged. Are there modifications I can make to the components to get a cleaner signal that is more of a line level than headphone level? I don’t need that much amplification for my application.

    #12678 Reply
    brach
    Moderator

    Nate,
    The schematic is at the end of the assembly manual (did you put your Macchiato together without the manual?).
    The noise of the audio amp can be dependent on the impedance of what it’s driving. It’s designed to drive low impedance loads, like speakers, not high impedance loads like a guitar amp or something, although it does fine in that capacity in most applications. So that might be causing some of the noise. From my experience, I’ve had to be mindful of the gain structure of the Macchiato and what it’s plugged into. Try keeping the volume very low on the Macchiato and boosting the input on what it’s plugged into…or vice versa if that doesn’t work. It all depends on how the impedance of the 2 devices match. But i’ve had good luck getting the noise floor low enough for recording by playing around with these levels.

    You asked about getting more of a line level rather than headphone level. There’s not much difference. Headphone level can just supply more current, but can usually get to around the same voltage level into higher impedances. But if you want, you can replace the the amp IC with a buffer (to reduce the noise caused by the amp IC). Disconnect pins 3 and 5 from the amp IC and hook in a unity gain buffer (either an opamp or emitter follower or something). You may want to disconnect R20 and R22 also if you don’t want those filters tainting the signal. You’ll want to remove the speaker too, so that the low impedance doesn’t strain the buffer.
    -Brach

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